SCHOOL VEHICLES (BLUE BACK)
When NJ converted from the blue plates to the graphic plates in 1991/1992, there were some unused blue plate blanks left over.
Reflective sheeting was applied to the blue blanks, so we have some reflective plates with a blue painted back.
W-S1 - Z-S1
5916AS1 has an unpainted aluminum back.
The blue back school vehicle plates appear to have started after the 7-digit series ended, so the first S1 plate was probably 100W-S1.
Even though I have only seen one plate in this series, we would assume the entire range 100W-S1 through 999Z-S1 had blue backs.
S1-A - S1-K
The blue backs continue from S1-A100 through the S1-K series.
The blue backs probably stopped at the changeover to the avery base.
If this is the case, S1-L100 was the first plate with an aluminum back.
(S1-L961 verified with an aluminum back.)
N-S2 - Z-S2
5265AS2 has a regular silver back.
The first blue back plate in the S2 series was probably 100N-S2 (this would have been the first one after the 7-digit series ended).
They continued through 999Z-S2.
The S2-A series was also made with blue backs.
The Avery base atarted at S2-B100. This is probably where the blue backs stopped.
(S2-C488 verified with an unpainted aluminum back.)